1. Field of the Invention
The invention is directed to ovens, and in particular, microwave ovens having an oven cavity and two doors and a conveyor belt passing through the oven cavity and the two doors.
2. Description of Related Art
Conveyorized ovens, convection and microwave, have been used in industry for many years to cook or thaw foods and provide heat for processing items such as food, rubber, and foundry cores. The xe2x80x9cmicrowavexe2x80x9d ovens generally operate at 915 MHZ or 2,450 MHZ because these frequencies are within narrow frequency bands designated by government agencies for such purpose. Conventionally, such apparatus operate at assigned frequencies of either 915 or 2,450 MHZ and the term xe2x80x9cmicrowavexe2x80x9d as used herein is intended to refer to that portion of the electromagnetic energy spectrum having wavelengths in the order of 1 meter to one millimeter and frequencies in excess of 300 MHZ.
In microwave ovens the energy fed to the oven interior, or oven cavity, preferably resonates in a plurality of modes achieved by suitable adjustment of the oven dimensions. Such resonant modes are loaded by absorption of heat by the item being heated, and such absorption varies with the absorbing characteristics of the item as well as its size and shape. To assure uniformity of heating it has generally been desirable to cyclically vary the mode pattern with respect to the article by, for example, a mechanical mode stirrer, by movement of the article within the oven, by varying the frequency of the energy fed to the enclosure, and/or combinations of all of the foregoing techniques. The multiplicity of modes, which vary with the loading within the oven and with the cyclical variation of the modes therein, can result in excitation of modes within the oven cavity. As such, prior conveyorized ovens utilized flaps or energy choke tunnels, also known as suppression tunnels, to decrease the amount of heat and microwaves that escape from the oven cavity during operation of the oven.
In fact, the intensity of microwave energy permitted to leak from domestic and/or industrial microwave heating systems is restricted. In the United States, for example, the Department of Health and Human Services requires that the microwave energy leakage from a domestic oven not exceed one milliwatt per square centimeter in the factory or five milliwatts per square centimeter in the home. In other words, in a plane at a distance of five centimeters from the microwave oven, the intensity of the microwave leakage cannot exceed one milliwatt in the factory, and five milliwatts in the home. Further, the Occupational Safety and Health Administration requires a microwave energy exposure of less than ten milliwatts per square centimeter. The International Microwave Power Institute has adopted a standard for intensity of microwave energy radiation leakage which is xe2x80x9cless than ten milliwatts per square centimeterxe2x80x9d. Furthermore, the Federal Communication Commission has regulations regarding the amount of out-of-band radiation permissible by a microwave oven. Accordingly, systems employing the use of microwave energy for processing of materials or cooking and thawing food must include apparatus to prevent the leakage of microwave energy from the enclosure.
Many industrial ovens, such as convection and microwave ovens, require that there be a continuous access opening into the cavity, so that materials may be transported through the cavity by a conveyor to achieve high throughput. The suppression of microwave energy and heat loss from these continuous access openings has presented problems which are much more complex than a batch-type microwave oven or convection oven that do not include a conveyor belt and that can be manually sealed using a door.
Accordingly, prior to the development of the present invention, there has been no oven or method of heating at least one item in the oven which: provides high throughput, decreases the amount of heat and/or microwave loss from the oven cavity, and operates automatically through the use of a programmable logic center thereby decreasing the number of operators for each oven. Therefore, the art has sought an oven and method of heating at least one item in the oven which: provides high throughput, decreases the amount of heat and/or microwave loss from the oven cavity, and operates automatically through the use of a programmable logic center thereby decreasing the number of operators for each oven.
In accordance with the invention the foregoing advantages have been achieved through the present oven for heating at least one food item comprising: an oven cavity having a plurality of oven cavity walls; an oven heat source disposed within the oven cavity; at least one door disposed along at least one of the plurality of oven cavity walls, whereby the at least one door permits access into the oven cavity, the at least one door having a plurality of open positions and a closed position; at least one conveyor belt passing through the at least one door and the oven cavity, whereby at least one food item placed on the at least one conveyor belt can be transported into, and out of, the oven cavity when the at least one door is in at least one of the plurality of open positions; at least one motor operatively associated with the at least one conveyor belt, whereby the at least one motor moves the conveyor belt, and a programmable logic center in communication with the at least one door and the at least one motor, whereby the programmable logic center controls the movement of the at least one door from the closed position to the plurality of open positions to permit the at least one food item to be transported into, or out of the oven cavity, and from the plurality of open positions to the closed position, the programmable logic center preventing the oven from heating the at least one food item when the at least one door is in the plurality of open positions.
A further feature of the oven is that the oven cavity may include two doors. Another feature of the oven is that the two doors may be disposed along different oven cavity walls. An additional feature of the oven is that the two doors may be disposed opposite each other. A further feature of the oven it that the two doors may be interlocked, whereby both doors simultaneously move from the closed position to the plurality of open positions, and from the plurality of open positions to the closed position. Another feature of the oven is that the oven heat source may be a magnetron for providing microwave energy in the oven cavity. An additional feature of the oven is that the oven may include at least one sensor disposed along the at least one conveyor belt, the at least one sensor being in communication with the programmable logic center. A further feature of the oven is that the at least one door may be associated with at least one rail disposed along the at least one oven cavity wall. Another feature of the oven is that the oven may include at least one door actuator in communication with the at least one door and operatively associated with the programmable logic center, whereby the at least one door actuator is controlled by the programmable logic center to move the at least one door from the closed position to one of the plurality of open positions and from one of the plurality of open positions to the closed position. An additional feature of the oven is that the at least one door actuator may be a hydraulic actuator.
In accordance with the invention the foregoing advantages have also been achieved through the present oven for heating at least one food item comprising: an oven cavity having a plurality of oven cavity walls; an oven heat source disposed within the oven cavity; an entrance door disposed along one of the plurality of oven cavity walls, whereby the entrance door permits access into the oven cavity, the entrance door having a plurality of open positions and a closed position; an exit door disposed along one of the plurality of oven cavity walls, whereby the exit door permits access into the oven cavity, the exit door having a plurality of open positions and a closed position a conveyor belt passing through the entrance door, the oven cavity, and the exit door, whereby at least one food item placed on the conveyor belt can be transported into, and out of, the oven cavity when the entrance door is in one of the plurality of open positions, and the at least one food item can be transported out of the oven cavity when the exit door is in one of the plurality of open positions; a motor operatively associated with the conveyor belt, whereby the motor moves the conveyor belt through the entrance door, the oven cavity, and through the exit door; and a programmable logic center operatively associated with the entrance door, the exit door, and the motor, whereby the programmable logic center controls: the movement of the entrance door from the closed position to one of the plurality of open positions to permit the at least one food item to be transported into the oven cavity; the movement of the entrance door from one of the plurality of open positions to the closed position; the oven heat source; the movement of the exit door from the closed position to one of the plurality of open positions to permit the at least one food item to be transported out of the oven cavity, the programmable logic center operable to prevent the oven heat source from heating the at least one food item when either the entrance door or the exit door is in one of the plurality of open positions.
A further feature of the oven is that the entrance door and the exit door may be interlocked, whereby both doors simultaneously move from the closed position to one of the plurality of open positions, and from one of the plurality of open positions to the closed position. Another feature of the oven is that the oven heat source may be a magnetron for providing microwave energy in the oven cavity. An additional feature of the oven is that the oven may include at least one sensor disposed along the conveyor belt, the at least one sensor being operatively associated with the programmable logic center. A further feature of the oven is that the entrance door and the exit door may each be operatively associated with at least one rail disposed along the at least one oven cavity wall. Another feature of the oven is that the at least one door actuator may be operatively associated with both the entrance door and the exit door and operatively associated with the programmable logic center, whereby the at least one door actuator is controlled by the programmable logic center to move the entrance door or the exit door from the closed position to one of the plurality of open positions and from one of the plurality of open positions to the closed position. An additional feature of the oven is that the at least one door actuator may be a hydraulic actuator.
In accordance with the invention, the foregoing advantages have also been achieved through the present method of heating at least one food item in an oven, the oven comprising an oven cavity, a plurality of oven cavity walls, at least one door disposed in at least one of the oven cavity walls, the at least one door having a plurality of open positions and a closed position, an oven heat source, at least one sensor, a programmable logic center, at least one motor, and at least one conveyor belt passing through the at least one door and the oven cavity, comprising the steps of: placing the at least one food item on the conveyor belt; sensing the at least one food item on the conveyor belt by the at least one sensor, sending a first signal from the at least one sensor to the programmable logic center; sending a second signal from the programmable logic center to the at least one door to confirm that the at least one door is in any of the plurality of open positions or to open the at least one door, if the at least one door is in the closed position; sending a third signal from the programmable logic center to activate the at least one motor, whereby the conveyor belt begins to move; moving the at least one conveyor belt through the at least one door, whereby the conveyor belt transports the at least one food item through the at least one door and into the oven cavity; sending a fourth signal from the programmable logic center to the at least one motor, whereby the at least one motor is stopped and the conveyor belt is stopped whereby the at least one food item is located within the oven cavity; sending a fifth signal from the programmable logic center to the at least one door, whereby the at least one door is moved from one of the plurality of open positions to the closed position; sending a sixth signal from the at least one door to the programmable, logic center to confirm that the at least one door is in the closed position; sending a seventh signal from the programmable logic center to the oven heat source, whereby the oven heat source is activated and the oven cavity is heated; heating the at least one food item for an amount of time sufficient to heat the at least one food item; sending an eighth signal from the programmable logic center to the oven heat source, whereby the oven heat source is deactivated; sending a ninth signal from the programmable logic center to the at least one door, whereby the at least one door is moved from the closed position to one of the plurality of open positions; sending a tenth signal from the programmable logic center to the at least one motor, whereby the conveyor belt begins to move; and moving the conveyor belt through the at least one door, whereby the conveyor belt transports the at least one food item through the at least one door and out of the oven cavity.
A further feature of the method of heating at least one item is that the at least one door may include at least one door actuator, the at least one door being moved from the closed position to one of the plurality of open positions, and from one of the plurality of open positions to the closed position, by sending an actuating signal from the programmable logic center to the at least one door actuator. Another feature of the method of heating at least one item is that the oven cavity may include two doors. An additional feature of the method of heating at least one item is that the two doors may be disposed along different cavity oven walls. A further feature of the method of heating at least one item is that the two doors may be disposed opposite each other.
In accordance with the invention, the foregoing advantages have also been achieved through the present method of heating at least one food item in an oven, the oven comprising an oven cavity, a plurality of oven cavity walls, at least one door disposed in at least one of the oven cavity walls, the at least one door having a plurality of open positions and a closed position, a continuously heating oven heat source, a first and a second sensor, a programmable logic center, at least one motor, and at least one continuously moving conveyor belt passing through the at least one door and the oven cavity, comprising the steps of: placing the at least one food item on the continuously moving conveyor belt; sensing the at least one food item on the continuously moving conveyor belt by the first sensor; sending a first signal from the first sensor to the programmable logic center; sending a second signal from the programmable logic center to the at least one door to confirm that the at least one door is in any of the plurality of open positions or to open the at least one door, if the at least one door is in the closed position; moving the at least one continuously moving conveyor belt through the at least one door, whereby the continuously moving conveyor belt transports the at least one food item through the at least one door and into the oven cavity; sending a third signal from the programmable logic center to the at least one door, whereby the at least one door is moved from one of the plurality of open positions to the closed position; sending a fourth signal from the at least one door to the programmable logic center to confirm that the at least one door is in the closed position; heating the at least one food item for an amount of time sufficient to heat the at least one food item; sending a fifth signal from the second sensor to the programmable logic center; sending a sixth signal from the programmable logic center to the at least one door, whereby the at least one door is moved from the closed position to one of the plurality of open positions; and moving the continuously moving conveyor belt through the at least one door, whereby the continuously moving conveyor belt transports the at least one food item through the at least one door and out of the oven cavity.
The oven and method of heating at least one item in the oven of the present invention have the advantages of: providing high throughput, decreasing the amount of heat and/or microwave loss from the oven cavity, and operating automatically through the use of a programmable logic center, thereby decreasing the number of operators for each oven.